The present disclosure relates to a controller and a control method for an internal combustion engine for estimating an exhaust gas temperature of the internal combustion engine.
In order to operate an internal combustion engine appropriately, it is important to accurately monitor state quantity, such as pressure and temperature of each part, which change according to operating condition of the internal combustion engine. In recent years, also using state quantity of the exhaust system, control of the internal combustion engine is performed. As a control using state quantity of the exhaust system, for example, enrichment control which makes air-fuel ratio rich to decrease exhaust gas temperature is performed, when there is a possibility of damaging a catalyst, an air-fuel ratio sensor, and the like, which are provided in the exhaust system, by rise of exhaust gas temperature at high rotation speed and high load operation. Although the exhaust gas temperature used for this control may be detected by an exhaust gas temperature sensor, there is also a method of estimating in order to reduce sensor cost. For example, by referring to map data in which a relationship among rotational speed, charging efficiency, and exhaust gas temperature is preliminarily set based on experimental data and the like, a method of estimating exhaust gas temperature is used.
As other examples using exhaust gas temperature, for example, in JP 5409832 B, although a method of calculating an intake air amount and an internal EGR rate of a combustion chamber using a volumetric efficiency corresponding value is disclosed, exhaust gas temperature is used for calculation of this volumetric efficiency corresponding value. Although a method of controlling an internal combustion engine with a supercharger is disclosed in JP 5963927 B, exhaust gas temperature is used for controlling an opening degree of wastegate required to achieve a target driving force of a compressor. In these documents, an estimation method of exhaust gas temperature using the similar map data as mentioned above is used. Besides these documents, exhaust gas temperature may be used for calculating a flow rate of external EGR based on an opening degree of an EGR valve.
Although the estimated exhaust gas temperature is used in the above-mentioned example; as an example using the exhaust gas temperature sensor, with strengthening of exhaust gas regulation, there is control which reduces emission amount of PM (Particulate Matter) included in exhaust gas of the internal combustion engine. Specifically, PM is caught by a particle collection filter attached to the exhaust system, such as DPF (Diesel Particulate Filter) and GPF (Gasoline Particulate Filter). However, since there is a limit on PM amount which the particle collection filter can catch, a regeneration process which burns PM accumulated in the particle collection filter is performed properly. In order to perform this regeneration process properly, exhaust gas temperature is controlled using the exhaust temperature sensor.